1. Field of the Invention
The invention pertains to the field of optical wavelength measuring instruments such as optical spectrum analyzers. It further pertains to techniques for calibrating optical wavelength measuring instruments.
2. Art Background
Optical instruments used for measuring wavelength, such as optical spectrum analyzers (OSA) are called upon to make measurements over a range of wavelengths. To verify the accuracy of these measurements, instrument calibration is necessary. Prior techniques involve calibrating the device of interest using a single wavelength standard, such as a calibrated source, or a known absorption pit in a gas cell. While calibration at a single point insures measurement accuracy at and near that single point, measurement accuracy over a wider range can only be implied or estimated. Particularly, single point calibration does not correct for any errors in linearity of the optical instrument over a wide wavelength range.
Wavelength measurement accuracy in an optical instrument over its wavelength range is improved by calibrating the instrument using many reference points. In a first embodiment of the invention, multiple calibration points are used to form an average correction factor. In a second embodiment of the invention, multiple reference points are used to fit a correction function applied over the wavelength range. This correction function may be linear, higher order, or periodic in nature. One correction function may be used over the range of the device, or the range may be segmented, and different correction values calculated and used for each segment.